Device for bending a straight tube into a circular shape



A. REIJNDERS Nov. 2, 1965 DEVICE FOR BENDING A STRAIGHT TUBE INTO A CIRCULAR SHAPE 2 Sheets-Sheet 1 Filed June 27, 1961 FIG.1

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INVENTOR. ANTON/US REIJNDERS FIG. 3

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A. REIJNDERS Nov. 2, 1965 DEVICE FOR BENDING A STRAIGHT TUBE INTO A CIRCULAR SHAPE Filed June 27, 1961 2 Sheets-Sheet 2 FIG.6

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United States Patent 3,215,518 DEVICE FOR BENDING A STRAIGHT TUBE INTO A QIRC'ULAR SHAPE Antonius Reijnders, Eindhoven, Netherlands, assiguor to North American Philips (Zompany, Inc., New York, N .Y., a corporation of Delaware Filed June 27, 1961, Ser. No. 119,883 Claims priority, application Netherlands, July 16, 1969, 253,892 2 Claims. (Cl. 65-281) Devices for bending a heated straight glass tube into a circular shape are known, which comprise means for holding the tube at its upper extremity, a bending roller rotatable in a yoke, means for securing the lower extremity of the tube to the periphery of the bending roller, means for vertically moving the yoke so that the tube is wound onto the circumference of the bending roller and also means for switching off the drive for the yoke when the yoke has arrived at a certain distance from its ultimate extreme upper position. Such devices permit of bending straight glass tubes into tubes of a circular shape, which are used, for example, as tubes for illumination purposes.

In known devices the yoke is driven directly by a chain which is set into motion by an electric motor. During rolling a straight heated tube onto the circumference of the bending roller, the drive for the chain is stopped at a given moment and the chain, together with the yoke, moves further over a certain length in a vertical direction due to inertial forces occurring in the system. For practical reasons it is desirable that the vertical movemerit of the yoke should not be reduced to zero with a shock.

It has been found that the distance still traversed by the yoke, due to the inertia, after the drive has been switched off, is diificult to maintain constant. This gives rise to considerable differences in length of the circularlybent product, resulting in a varying radius of curvature of the bent tube and/ or locally undesirable deformation.

An object of the invention is to provide a device in which the path covered by the yoke may be maintained constant.

A device according to the invention is characterized in that the means for moving the yoke comprise a driving rod, the first extremity of which is coupled to the yoke and movable in a vertical direction and the second extremity of which is movable along a closed path having a portion along which the second extremity of the driving rod can move so that the first extremity is substantially at rest, While the means for switching off the drive are arranged so that, after switching off, the second extremity of the driving rod comes to a standstill in the said portion of the path. Thus, use is made as it were of a kind of crank-driving rod mechanism for driving the yoke, the means for driving the crank not being connected directly to the yoke. The distance which can be covered by the yoke in a vertical direction is determined by the shape of the closed path. After the straight tube is rolled onto the bending roller rotatable in the yoke and the yoke has reached its highest position, it must be maintained in this position for a certain period in order to remove the bent object from the bending roller. For this purpose, in a device according to the invention also the drive is already switched ofi before the yoke has reached its highest position. The means for switching off are arranged in the vicinity of the said portion of the path at an area such that the extremity of the driving rod coupled to the yoke remains substantially in its extreme vertical posiiton over the length over which the second extremity of the driving rod traverses this portion of the path, due to inertial forces, at a speed decreasing to zero.

In another embodiment, means, which may be adjustable, are provided near the said portion of the path for limiting the distance traversed by the second extremity of the driving rod along this portion of the path at decreasing speed, so that at the moment when this extremity of the rod has come to a standstill, the yoke finds itself at the point of reversal of its vertical movement. It is thus ensured that the path covered by the yoke during rolling is highly constant for each tube to be bent. As a rule, the second extremity of the driving rod, which can move along the said portion of the path, comes to a standstill with a shock. However, this is by no means objectionable since at the moment when such shock occurs, the extremity of the driving rod coupled to the yoke has already reached its extreme vertical position. Preferably the means for limiting the distance to be covered along the closed path are arranged so that this path is divided into portions of approximately equal length.

In order that the invention may be readly carried into effect, one embodiment thereof will now be described in detail, by way of example, with reference to the accompanying diagrammatic drawings, in which:

FIGURE 1 shows a straight glass tube which must acquire a circular shape by bending;

FIGURE 2 is a side view of a device for bending heated glass tubes into a circular shape. FIGURES 3, 4 and 5 show the essential parts of the device separately, 1.e.

FIG. 3 shows the stationary portion,

FIG. 4 shows the oven portion displaceable with respect thereto and FIG. 5 shows the bending portion which is likewise displaceable.

FIG. 6 shows a portion of the cross-section, taken along the line VIVI of FIGURE 5.

FIG. 7 is a diagrammatic view of the elements associated with the driving mechanism for the bending device.

Referring now to FIGURE 1, a straight glass tube 1 has, at each extremity, a sealed lamp stem 2, a metal plate 3 and an exhaust tube 4. The tube 1 may be deformed by a known method into a shape indicated by 5. For this purpose the straight tube together with the plate 3 is inserted into a holder 7 so as to hang vertically in it. Subsequently, the tube is heated in an oven and bent into a circular shape by means of a bending roller. During heating, nitrogen is introduced into the interior of the tube through one of the exhaust tubes 4, thus avoiding oxidation of the cathode parts inside the tube. Furthermore the pressure in the tube is raised both during and after bending, in order to maintain the circular shape of the cross-section.

This method may be carried out in a device as shown diagrammatically in FIGURE 2. The stationary portion thereof (FIGURE 3) comprises a frame having two guides 14. The holder 7, in which the tube 1 to be deformed can be suspended, is arranged in the frame at its upper end. The means for supplying nitrogen to the interior of the tube are omitted in FIGURE 3 for the sake of simplicity. V

The movable oven portion shown in FIGURE 4 comprises a carriage which can run on guides 14 and which carries a frame with an oven 12. The oven comprises two halves which are removable from each other. Upon displacement to the right, the oven is opened and not closed until it contains the tube 1. When the tube is heated and plasticized in the oven 12, it acquires a greater length. In order to ensure that the variation in length can be properly regulated, use is made of a test device provided on the stationary portion (FIGURE 3). A pin 11 is arranged to be slidable in a longitudinal direction so as to bear against the lower end of the tube 1 while exerting a small force. As the tube 1 becomes longer, the pin 11 invariably exerts substantially the same small force upon the tube, since the pin 11 forms part of a sensitive balance comprising substantially a lever 8 with counterweight 9, which is pivoted at a fixed point 10.

The bending portion of the device shown in FIG. comprises a structure which can likewise run on the guides 14 and which carries the bending portion of the device. This portion comprises a bending roller 23 which is rotatable in a yoke 24. The yoke 24 is displaceable in a vertical direction over rods 44 and 45 relative to the carriage 16 (see also FIG. 6).

The means for displacing the yoke 24 in a vertical direction and for rotating the bending roller 23 in the yoke are shown diagrammatically in FIGURES 5, 6 and 7. The yoke 24 is secured to a chain 22 which is movable over two chain wheels 20 and 21. Secured to the chain 22 is a mass 25 which serves as a counterweight for the yoke and the bending roller. According to the invention, the means for driving this chain comprise a driving rod 26, the first extremity of which is secured to the counterweight 25 and the other extremity of which is secured by means of a junction block 41 to a chain 27. The latter chain, which is movable over chain wheels 28 and 29, is maintained stretched at two areas by means of rollers 30. The chain wheel 29 is driven by means of an electric motor 32, a worm housing 33 and a rope transmission 31. A band brake is indicated diagrammatically by 59. The direction of movement of the chain 27 is invariably the same.

Sets of gear wheels 36, 37 and 38 are rotatably arranged in the yoke 24 (see FIGURES 6 and 7). By movement of the chain 22,,the yoke can slide over guide rods 44 and 45 and the bending roller 23 provided in the yoke can perform a rotation due to the set of gear wheels 38 meshing with a set of toothed rods 35 fixedly arranged relative to the carriage 16.

The device operates as follows:

After the tube 1 has been heated in the oven, displaced to the right, and has expanded up to a certain length while being supported on the pin 11, the carriage 16 together with the bending device is rapidly moved to the left while at the same time the oven 12 with its halves open is displaced to the left. At the end of this movement, the bending roller 23 abuts the lower end of the tube 1 in a manner shown in FIGURE 5 and the metal plate 3 of the tube 1 may be clamped in position on the periphery of the bending roller 23 by means of clamps provided on the bending roller 23. An electromagnet 17 subsequently displaces the pin 11 rapidly downwards. The electric .motor 32 is then switched on and drives the chain 27 together with the junction block at first at accelerated speed and then at uniform speed in a direction indicated by an arrow 40. Due to the presence of driving rod 26, the counterweight 25 and the yoke 24 perform a translation and the bending roller 23 in the yoke starts to rotate, thus causing the tube 1 to be rolled onto the circumference thereof.

After switching on the electric motor 32, the block 41 first traverses the curved portion of the path, indicated by 43, with the result that the speed of the chain 22, apart from the starting acceleration of the motor, increases approximately in a sinusoidal manner. When the block 41 has covered a portion 43 of the path, the upper extremity of the driving rod and the yoke 24 move on at approximately uniform speed. Due to the presence of a curved portion 46 of the path, the speed of the ascending yoke 24 decreases approximately sinusoidally to zero and the yoke reaches the point of reversal of its vertical movement. Since the yoke must be maintained in this extreme position for some time, in order to remove the rolled tube 1 from the bending roller, the energization of the electric motor 32, before the yoke reaches the point of reversal of its motion, is switched off by a switch 56 operated by an arm 58, otherwise adjustable, which is provided on the counterweight 25. The switch 56 is positioned at an area of the path to be covered by the counterweight 25 such that, due to the inertial forces occurring in the system, the block 41 comes to a standstill in the portion 46 of the path when the yoke has reached the point of reversal of its vertical movement. Due to the great curvature in the portion 46 of the path, a standstill of the lower extremity of the driving rod at an area situated to the left or to the right of the position indicated by 50, gives little rise to the upper extremity of the driving rod to occupy a position differing from the extreme vertical position.

After the tube 1 has been wound onto the bending roller, the roller halves can be relatively moved by movement of levers 63, each pivoted on a spindle 59, in the direction indicated by an arrow 65, whereupon the circularly-bent product can be removed.

In order to ensure that the counterweight is exactly at the point of reversal of its vertical movement at the moment when the block 41 has come to a standstill and that even very small differences from the extreme vertical position of the counterweight 25 and the yoke 24 are avoided, the portion 46 of the path may be provided with a stop 54 against which the junction block, which moves along this portion of the path at a decreasing speed, ultimately comes to a standstill with a shock. Since the upper extremity of the driving rod than has reached exactly the point of reversal of its movement, such shock will not be transferred to the bending roller. The tube wound onto the bending roller thus always has the same length, as reckoned along its circumference. The abutment 54 is provided on an arm 66 which is pivoted at a fixed point 51 and which is pivotally connected to a lever 53, which in turn is pivotally connected to an arm 69 pivoted at a second fixed point 68. The abutment 54 is maintained pushed in the path traversed by the block 41 by the action of a compression spring 70.

The yoke 24 is moved back to its initial position by turning the lever 53 in the direction indicated by an arrow 71, resulting in a switch 62 being operated which re-energizes the electric motor 32. The chain 27 is then moved on again and the upper extremity 25 of the driving rod performs an ascending movement. Near the end of the movement of the yoke, the arm 57, connected to the counterweight 25, can operate another switch 64 which stops the energization of the electric motor 32. In the meantime the block 47, situated farther a distance equal to half the length of the chain, has arrived on the curved portion of the path and can move over this portion of the path at a decreasing speed, until it abuts with a shock against the stop 54 which has in the meantime been moved back into the portion 46 of the path. The whole cycle may then be repeated again.

What is claimed is:

1. A device for bending a heated straight glass tube into a circular shape comprising means for holding the tube at its upper end, a yoke, a bending roller, means mounting said bending roller in said yoke for rotation therein, means for securing the lower end of said tube to the periphery of said bending roller, a first drive means for moving said yoke in a substantially vertical direction whereby said tube is bent about the circumference of said bending roller, switching means for switching off said first drive means when said yoke has moved vertically to a predetermined position at a certain distance from its ultimate extreme upper position, a switch actuator on said first drive means, a second drive means including a driving rod having one end coupled to said first drive means and movable in a vertical direction and another end which moves along a closed path having a portion along which said other end of said driving rod can move so that said one end is substantially at a rest position, said switch actuator being so arranged that when it is in a predetermined location in space said one end of the driving rod is at rest and said switching means is switched oif by said switch actuator to thereby stop said first and second drive means, and means adjacent to the portion of said path for limiting the length traversed by said other end of the driving rod along the said portion of said path at decreasing speed whereby at the moment when said other end of said driving rod comes to said rest position said yoke is located at the point of reversal of its vertical motion.

2. A device for bending a heated straight glass tube into a circular shape as claimed in claim 1 wherein said means adjacent to the portion of the path for limiting the length traversed by said other end of the driving rod along said portion of the path at decreasing speed is a pivoting arm having an abutment therein, and a spring fixed at one end and secured at the other end to said arm thereby biasing said abutment in the path of travel of said other end of the driving rod.

References Cited by the Examiner UNITED STATES PATENTS 283,142 8/83 Reid 74-37 1,637,078 7/27 H111 7437 1,970,620 8/34 Park 7437 2,491,857 12/49 Greiner 65-278 X 2,494,872 1/50 Greiner et a1 65-110 X 2,608,697 9/52 Condemi 74-37 2,611,216 9/52 Snow et a1. 65280 X DONALL H. SYLVESTER, Primary Examiner. 

1. A DEVICE FOR BENDIG A HEATED STRAIGHT GLASS TUBE INTO A CIRCULAR SHAPE COMPRISING MEANS FOR HOLDING THE TUBE AT ITS UPPER END, A YOKE, A BENDING ROLLER, MEANS MOUNTING SAID BENDING ROLLER IN SAID YOKE FOR ROTATION THEREIN, MEANS FOR SECURING THE LOWER END OF SAID TUBE TO THE PERIPHERY OF SAID BENDING ROLLER, A FIRST DRIVE MEANS FOR MOVING SAID YOKE IN A SUBSTANTIALLY VERTICAL DIRECTION WHEREBY SAID TUBE IS BENT ABOUT THE CIRCUMFERENCE OF SAID BENDING ROLLER, SWITCHING MEANS FOR SWITCHING OFF SAID FIRST DRIVE MEANS WHEN SAID YOKE HAS MOVED VERTICALLY TO A PREDETERMINED POSITION AT A CERTAIN DISTANCE FROM ITS ULTIMATE EXTREME UPPER POSITION, A SWITCH ACTUATOR ON SAID FIRST DRIVE MEANS, A SECOND DRIVE MEANS INCLUDING A DRIVING ROD HAVING ONE END COUPLED TO SAID FIRST DRIVE MEANS AND MOVABLE IN A VERTICAL DIRECTION AND ANOTHER END WHICH MOVES ALONG A CLOSED PATH HAVING A PORTION ALONG WHICH SAID OTHER END OF SAID DRIVING ROD CAN MOVE SO THAT SAID ONE END IS SUBSTANTIALLY AT A REST POSITION, SAID SWITCH ACTUATOR BEING SO ARRANGED THAT WHEN IT IS IN A PREDETERMINED LOCATION IN SPACE SAID ONE END OF THE DRIVING ROD IS AT REST AND SAID SWITCHING MEANS IS SWITCHED OFF BY SAID SWITCH ACTUATOR TO THEREBY STOP SAID FIRST AND SECOND DRIVE MEANS, AND MEANS ADJACENT TO THE PORTION OF SAID PATH FOR LIMITING THE LENGTH TRAVERSED BY SAID OTHER END OF THE DRIVING ROD ALONG THE SAID PROTION OF SAID PATH AT DECREASING SPEED WHEREBY AT THE MOMENT WHEN SAID OTHER END OF SAID DRIVING ROD COMES TO SAID REST POSITION SAID YOKE IS LOCATED AT THE POINT OF REVERSAL OF ITS VERTICAL MOTION. 